Dual position DC magnetron assembly

ABSTRACT

A sputtering system includes a first sputtering assembly configured to sputter material onto a first disk and a second sputtering assembly configured to sputter material onto a second disk, the second sputtering assembly positioned proximate the first sputtering assembly. The first sputtering assembly includes a first magnetic ring, and the second sputtering assembly includes a second magnetic ring. The first magnetic ring includes a first region of lower relative magnetic strength positioned near the second magnetic ring, and the second magnetic ring includes a second region of lower relative magnetic strength positioned near the first magnetic ring.

REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 12/368,951, entitled “DUAL POSITION DC MAGNETRON ASSEMBLY,” which was filed on Feb. 10, 2009, and is incorporated by reference in its entirety.

BACKGROUND

A variety of equipment may be used in the manufacture of disk drive media to form the different magnetic and non-magnetic layers. In a typical process, a glass or aluminum substrate travels sequentially through a number of stations at which different materials are deposited under different conditions. For example, one or more sputtering systems may be used to sputter magnetic and/or non-magnetic materials onto the media.

In conventional sputtering processes, active sputtering stations for the media must be separated by relatively large distances. Without such separation, electromagnetic interference might occur between the stations and result in inhomogeneous sputtering or even equipment failure. Thus, the sputtering stations are physically separated, or, if closely situated, the sputtering stations may not be not used concurrently. Indeed, in some sputtering systems, sputtering components may be shared between adjacent sputtering stations and may be moved back and forth between them as the active sputtering station changes.

Unfortunately, such separation (whether physical or temporal) may result in increased capital expenditure, wasted manufacturing floor space and/or slower throughput. There is therefore a need for an improved sputtering system having at least two sputtering locations proximate one another.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional, schematic view illustrating an exemplary sputtering system including two disks in corresponding sputtering locations, according to one embodiment.

FIG. 2 is a top, schematic view illustrating one side of the sputtering system of FIG. 1, according to one embodiment.

FIG. 3 is a perspective, schematic view illustrating an exemplary magnetic ring for use in the sputtering system of FIG. 1, according to one embodiment.

FIG. 4 is a top, schematic view illustrating the exemplary magnetic ring of FIG. 3, according to one embodiment.

FIG. 5 is a top, schematic view illustrating exemplary magnetic rings for use in the sputtering system of FIG. 1, with shaded regions of lower relative magnetic strength, according to one embodiment.

FIG. 6 illustrates a flow chart for a method of manufacturing magnetic disks, according to one embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1, an exemplary sputtering system 100 is illustrated, according to one embodiment. The sputtering system 100 includes a first sputtering assembly 102 a configured to sputter material onto a first disk 104 a and a second sputtering assembly 102 b configured to sputter material onto a second disk 104 b. As illustrated, the second sputtering assembly 102 b is positioned proximate the first sputtering assembly 102 a. The first sputtering assembly 102 a may include a first anode 106 a, a first cathode 108 a, a first target 110 a coupled to at least one of the first anode 106 a and the first cathode 108 a, and a first magnetic ring 112 a. Meanwhile, the second sputtering assembly 102 b may include a second anode 106 b, a second cathode 108 b, a second target 110 b coupled to at least one of the second anode 106 b and the second cathode 108 b, and a second magnetic ring 112 b. In one embodiment, the first magnetic ring 112 a includes a first region 114 a of lower relative magnetic strength positioned near the second magnetic ring 112 b, and the second magnetic ring 112 b includes a second region 114 b of lower relative magnetic strength positioned near the first magnetic ring 112 a.

The sputtering system 100 may comprise any of a variety of systems configured to sputter materials in different environments. The sputtering system 100 may be configured for RF, DC or pulsed-DC magnetron sputtering. In other embodiments, other sputtering methods may be implemented in the sputtering system 100. In one embodiment, as illustrated, the sputtering system 100 includes two sputtering locations at which disks 104 a, b may be positioned within a sealed chamber. In other embodiments, the sputtering system 100 may include three or more sputtering locations for accommodating greater numbers of disks or other media.

As illustrated, the sputtering system 100 is configured to sputter materials onto a pair of magnetic disks 104 a, b, and the methods described herein will be described in terms of such a system. Such magnetic disks 104 a, b may comprise the media used in conventional disk drives, and may include any of a variety of magnetic and non-magnetic materials deposited onto a substrate (e.g., glass or aluminum). However, the methods and components described herein may also be applied to and/or implemented in other sputtering systems, including, e.g., systems used to sputter materials onto optical and magneto-optical disks or onto differently shaped substrates used in other environments.

In one embodiment, the sputtering system 100 may further comprise a third sputtering assembly 102 c configured to sputter material onto the first disk 104 a and a fourth sputtering assembly 102 d configured to sputter material onto the second disk 104 b. As illustrated, the third sputtering assembly 102 c is positioned opposite the first sputtering assembly 102 a, and the fourth sputtering assembly 102 d is positioned opposite the second sputtering assembly 102 b. The third sputtering assembly 102 a may include a third anode 106 c, a third cathode 108 c, a third target 110 c coupled to at least one of the third anode 106 c and the third cathode 108 c, and a third magnetic ring 112 c. Similarly, the fourth sputtering assembly 102 d may include a fourth anode 106 d, a fourth cathode 108 d, a fourth target 110 d coupled to at least one of the fourth anode 106 d and the fourth cathode 108 d, and a fourth magnetic ring 112 d. In one embodiment, the third magnetic ring 112 c includes a third region of lower relative magnetic strength positioned near the fourth magnetic ring 112 d, and the fourth magnetic ring 112 d includes a fourth region of lower relative magnetic strength positioned near the third magnetic ring 112 c.

Thus, in one embodiment, the sputtering system 100 may include substantially identical pairs of sputtering assemblies 102 a-d positioned opposite one another. As illustrated, these sputtering assemblies 102 a-d may be configured such that both sides of the first and second disks 104 a, b may be sputtered substantially concurrently. However, in other embodiments, the sputtering system 100 may be configured to sputter onto only one side of the disks 104 a, b at a time.

The first sputtering assembly 102 a includes a first anode 106 a and a first cathode 108 a. As illustrated, the first anode 106 a is positioned along a central axis of the first sputtering assembly 102 a. The first cathode 108 a is arranged peripherally about the first anode 106 a and is electrically coupled to the first target 110 a. In such an embodiment, positive ions created in the sputtering system 100 are attracted to and bombard the surface of the first target 110 a, and material is thus ejected from the first target 110 a during the sputtering operation to be deposited onto the first disk 104 a. The first anode 106 a is generally circular when viewed from the top (as visible in FIG. 2), while the first cathode 108 a is generally disk-shaped. Of course, the geometry and polarity of these portions of the first sputtering assembly 102 a may be changed in different embodiments to achieve different sputtering characteristics. For example, in one embodiment, the first anode 106 a may be arranged peripherally about the first cathode 108 a and may be coupled to the first target 110 a.

In one embodiment, the first anode 106 a is electrically coupled to ground, and the first cathode 108 a is configured to reach an electrical potential of less than −300 V. For example, the first cathode 108 a may be kept at an electrical potential of approximately −500 V. In other embodiments, any of a variety of electrical potentials may be employed for the first anode 106 a and the first cathode 108 a to achieve the desired sputtering characteristics.

In one embodiment, the other anodes 106 b-d and cathodes 108 b-d may be configured substantially similarly to the first anode 106 a and first cathode 108 a. Thus, in one embodiment, the above description of the first anode 106 a and the first cathode 108 a may be applied equally to any of the anodes 106 b-d and cathodes 108 b-d. In other embodiments, different geometries and electrical potentials may be used for the anodes 106 and cathodes 108 in the different sputtering assemblies 102 (e.g., in order to sputter different materials onto the disks 104 a, b).

The first and second targets 110 a, b may comprise any of a variety of materials. In one embodiment, the first and second targets 110 a, b include magnetic alloys (e.g., Cobalt, Iron, Nickel), and may be used to sputter such magnetic alloys onto the first and second disks 104 a, b. In other embodiments, the first and second targets 110 a, b may include non-magnetic materials (e.g., Chrome, Carbon). Each of the targets 110 a, b may be substantially disc-shaped in order to facilitate relatively homogeneous sputtering onto the disks 104 a, b. The geometry of the first and second targets 110 a, b may be better understood with reference to FIG. 2, which shows a top view of the first and second sputtering assemblies 102 a, b. In one embodiment, the targets 110 a, b each have a diameter greater than that of the first and second disks 104 a, b. In other embodiments, other geometries for the first and second targets 110 a, b may be used to achieve different sputtering characteristics.

The first target 110 a may be electrically coupled to the first cathode 108 a, and the second target 110 b may be electrically coupled to the second cathode 108 b. As illustrated in FIG. 1, the first target 110 a may be received by and positioned in direct contact with the first cathode 108 a. When a new target is needed, the first target 110 a may be removed and replaced with a fresh target for additional sputtering. In other embodiments, other structures may be used to electrically couple the first target 110 a to the first cathode 108 a. Similar structures may also be used to electrically couple the second target 110 b to the second cathode 108 b.

In one embodiment, the third and fourth targets 110 c, d may be configured substantially similarly to the first and second targets 110 a, b. Thus, in one embodiment, the above description of the first and second targets 110 a, b may be applied equally to any of the targets 110 c, d. In other embodiments, different geometries, materials and electrical coupling structures may be used for the targets 110 of the different sputtering assemblies 102 (e.g., in order to sputter different materials onto the disks 104 a, b).

As illustrated, the first sputtering assembly 102 a is positioned proximate the second sputtering assembly 102 b. For example, in one embodiment, the first target 110 a and the second target 110 b may be positioned such that a central axis of the first target 110 a is spaced apart from a central axis of the second target 110 b by approximately 15 cm. Such spacing may be used, for example, when sputtering to 95 mm media used in magnetic disk drives. In other embodiments, the first target 110 a and the second target 110 b may be positioned closer or farther away, depending upon the size of the disks 104 a, b and overall geometry of the sputtering system 100.

In one embodiment, the first cathode 108 a may be positioned less than 3 cm apart from the second cathode 108 b. Indeed, the first cathode 108 a may be positioned less than 1.5 cm apart from the second cathode 108 b. In order to bring these highly charged components so close together, the sputtering system 100 may further comprise a vacuum insulator 116 a positioned between the first cathode 108 a and the second cathode 108 b. In one embodiment, the vacuum insulator 116 a may comprise TEFLON®, manufactured and sold by DuPont. In other embodiments, the vacuum insulator 116 a may comprise DELRIN®, also manufactured and sold by DuPont. In some embodiments, the sputtering system 100 may further comprise a first anode vacuum insulator 118 a positioned between the first anode 106 a and the first cathode 108 a, as well as a second anode vacuum insulator 118 b positioned between the second anode 106 b and the second cathode 108 b. The first and second anode vacuum insulators 118 a, b may be formed from the same materials as the vacuum insulator 116 a.

The geometry of and spacing between the first and second sputtering assemblies 102 a, b may be similar to the geometry and spacing of the third and fourth sputtering assemblies 102 c, d. Thus, in one embodiment, the above description of the first and second sputtering assemblies 102 a, b may be applied equally to the third and fourth sputtering assemblies 102 c, d. For example, the sputtering system 100 may include a second vacuum insulator 116 b positioned between the third and fourth cathodes 108 c, d. The third and fourth sputtering assemblies 102 c, d may also include respective third and fourth anode vacuum insulators 118 c, d.

The sputtering system 100 may further include a plurality of magnetic rings 112 a-d to enable magnetron sputtering. The geometry and configuration of these magnetic rings 112 a-d may be better understood with reference to FIGS. 3-5, which illustrate exemplary magnetic rings 112 separated from the other components of the sputtering system 100.

In one embodiment, the first magnetic ring 112 a includes a first plurality of permanent magnets 120 a, and the second magnetic ring 112 b includes a second plurality of permanent magnets 120 b (as illustrated in FIGS. 3-5). These permanent magnets 120 a, b may be arranged to form substantially continuous magnetic rings 112 a, b. That is, in one embodiment, each of the first plurality of permanent magnets 120 a may be in mating contact with adjacent permanent magnets 120 a to either side, as shown in FIG. 5. In other embodiments, the first magnetic ring 112 a may not be continuous but may include one or more gaps in the ring, where the first plurality of permanent magnets 120 a are not in close contact. In addition, although illustrated as a perfect circle, the first and second magnetic rings 112 a, b need not be perfectly circular. For example, in one embodiment, each of the magnetic rings 112 a, b may be generally elliptical.

As illustrated, in one embodiment, the first plurality of permanent magnets 120 a may be affixed to a first carrying plate 122 a to form the first magnetic ring 112 a. Similarly, the second plurality of permanent magnets 120 b may be affixed to a second carrying plate 122 b to form the second magnetic ring 112 b. The permanent magnets 120 a, b may be affixed to the carrying plates 122 a, b using adhesive or other mechanical fasteners. In other embodiments, the first carrying plates 122 a may be omitted, and the first plurality of permanent magnets 120 a may be affixed one to the other to form the first magnetic ring 112 a. Other structures for forming the magnetic rings 112 a, b may also be used.

The first and second plurality of permanent magnets 120 a, b may comprise any of a variety of magnetic materials. In one embodiment, the permanent magnets 120 a, b comprise a magnetic alloy including Neodymium, Iron and Boron in any of a variety of ratios. In another embodiment, a magnetic alloy of Samarium and Cobalt may be used.

Of course, in other embodiments, the first and second magnetic rings 112 a, b may be formed from other magnetic structures. In one embodiment, a unitary ring of permanent magnetic material is used to form each of the first and second magnetic rings 112 a, b. In another embodiment, the first and second magnetic rings 112 a, b may each comprise one or more electromagnets.

In one embodiment, as illustrated in FIG. 5, the first and second magnetic rings 112 a, b include regions 114 a, b of lower relative magnetic strength. If the first and second magnetic rings 112 a, b comprise corresponding pluralities of permanent magnets 120 a, b, the first region 114 a of lower relative magnetic strength may include at least one permanent magnet 124 a (shaded in FIG. 5) that is weaker than other magnets of the first plurality of permanent magnets 120 a. Similarly, the second region 114 b of lower relative magnetic strength may include at least one permanent magnet 124 b that is weaker than other magnets of the second plurality of magnets 120 b. In the absence of these weaker regions 114 a, b, the magnetic field of the first magnetic ring 112 a might be asymmetrical, distorted by a bucking effect caused by the interaction between magnetic fields generated by the first and second magnetic rings 112 a, b. Similarly, the magnetic field of the second magnetic ring 112 b might also be asymmetrical. Thus, the weakened regions 114 a, b may be configured to compensate for the bucking effect, and allow the magnetic fields of each of the magnetic rings 112 a, b to be made substantially symmetrical.

In one embodiment, the weaker permanent magnets 124 a, b may be less than 10% weaker than the other permanent magnets 120 a, b. In another embodiment, the weaker permanent magnets 124 a, b may be approximately 5% weaker than the other permanent magnets 120 a, b. In still another embodiment, the weaker permanent magnets 124 a, b may be at least 1% weaker than the other permanent magnets 120 a, b. Although three permanent magnets 124 a, b of each magnetic ring 112 a, b are illustrated as weaker in FIG. 5, more or fewer permanent magnets may be made weaker in different embodiments to achieve the desired magnetic fields.

In other embodiments, different structures and/or magnetic configurations may be used to form the regions 114 a, b of lower relative magnetic strength. For example, in one embodiment, regions of the magnetic rings 112 a, b may be shunted in order to modify the shape of the magnetic fields generated by the magnetic rings 112 a, b and thereby decrease the effective magnetic strength of such regions 114 a, b. In other embodiments, additional, repelling magnets may be arranged relative to the magnetic rings 112 a, b in order to modify the shape of the magnetic fields generated by the magnetic rings 112 a, b. In still other embodiments, a location or size of one or more of the permanent magnets 120 a, b may be modified in order to achieve a lower relative magnetic strength.

In one embodiment, the first sputtering assembly 102 a further includes a first inner magnetic ring 126 a concentric with and positioned within the first magnetic ring 112 a, and the second sputtering assembly 102 b includes a second inner magnetic ring 126 b concentric with and positioned within the second magnetic ring 112 b. These pairs of magnetic rings 112 a, b, 126 a, b may be configured to create magnetic fields that improve efficiency during magnetron sputtering. In one embodiment, the inner magnetic rings 126 a, b comprise permanent magnets configured similarly to the permanent magnets 120 a, b that form the magnetic rings 112 a, b. In other embodiments, different magnetic structures may be used to form the inner magnetic rings 126 a, b. In one embodiment, the first magnetic ring 112 a is oriented such that a north pole of the first magnetic ring 112 a is configured to face the first disk 104 a, and the first inner magnetic ring 126 a is oriented such that a south pole is configured to face the first disk 104 a. The second magnetic ring 112 b and the second inner magnetic ring 126 b may be oriented similarly. Of course, in other embodiments, alternative orientations for the magnetic rings 112 a, b, 126 a, b may be employed.

The other magnetic rings 112 c, d and inner magnetic rings 126 c, d may be configured substantially similarly to the first and second magnetic rings 112 a, b and first and second inner magnetic rings 126 a, b. Thus, in one embodiment, the above description of the first and second magnetic rings 112 a, b and the first and second inner magnetic rings 126 a, b may be applied equally to the other magnetic rings 112 c, d and inner magnetic rings 126 c, d. In other embodiments, different geometries and structures may be used for the magnetic rings 112 c, d and inner magnetic rings 126 c, d in the other sputtering assemblies 102 c, d.

FIG. 6 illustrates a flow chart for a method 600 of manufacturing magnetic disks, according to one illustrated embodiment. This method 600 will be discussed in the context of the sputtering system 100 of FIGS. 1-5. However, the acts disclosed herein may be executed using any sputtering system, in accordance with the described method. Moreover, although described in the context of manufacturing magnetic disks, the acts of method 600 may also be carried out in other contexts. For example, acts of method 600 may be carried out to manufacture optical or magneto-optical disks.

As described herein, many of the acts comprising the method 600 may be orchestrated by a processor according to an automatic manufacturing algorithm, based at least in part on computer-readable instructions stored in computer-readable memory and executable by the processor. Of course, a manual implementation of one or more acts of the method 600 may also be employed.

At act 602, a sputtering system 100 is provided. The sputtering system 100 has a first target 110 a and a first magnetic ring 112 a associated with the first target 110 a, and a second target 110 b and a second magnetic ring 112 b associated with the second target 110 b. The first magnetic ring 112 a includes a first region 114 a of lower relative magnetic strength positioned near the second magnetic ring 112 b, and the second magnetic ring 112 b includes a second region 114 b of lower relative magnetic strength positioned near the first magnetic ring 112 a. In one embodiment, the sputtering system 100 may comprise one among a number of sputtering systems used in the manufacture of magnetic disks 104 a, b.

At act 604, a first disk 104 a is positioned at a first sputtering location 128 a within the sputtering system 100, the first sputtering location 128 a associated with the first target 110 a. At act 606, a second disk 104 b is positioned at a second sputtering location 128 b within the sputtering system 100, the second sputtering locations 128 b associated with the second target 110 b, the second sputtering location 128 b proximate the first sputtering location 128 a. In one embodiment, the first and second disks 104 a, b may be positioned at these sputtering locations 128 a, b using one or more movable disk carriers. In another embodiment, the first and second disks 104 a, b may be loaded onto respective holders at the sputtering locations 128 a, b using a robotic arm. In other embodiments, other mechanisms (manual or automatic) may be used to position the first and second disks 104 a, b at the sputtering locations 128 a, b. Acts 604 and 606 may be carried out substantially concurrently or at different times.

At act 608, a first electrical potential difference is generated between a first anode 106 a and a first cathode 108 a associated with the first sputtering location 128 a, and, at act 610, a second electrical potential difference is generated between a second anode 106 b and a second cathode 108 b associated with the second sputtering location 128 b. As described above, in one embodiment, generating the first electrical potential difference may include bringing the first anode 106 a to a ground potential and bringing the first cathode 108 a to a potential of less than −300V. The second electrical potential difference may be generated similarly. In other embodiments, different electrical potential differences may be generated.

At act 612, material is concurrently sputtered from the first target 110 a onto the first disk 104 a, and from the second target 110 b onto the second disk 104 b. Thus, in one embodiment, the sputtering system 100 may enable increased throughput by sputtering to multiple disks concurrently.

In some embodiments, as illustrated in FIG. 1, the method 600 may further comprise concurrently sputtering material from a third target 110 c onto an opposite surface of the first disk 104 a, and from a fourth target 110 d onto an opposite surface of the second disk 104 b. These acts may be executed concurrently with act 612.

In one embodiment, the method 600 may further comprise eroding a first approximately circular race track pattern in the first target 110 a and a second approximately circular race track pattern in the second target 110 b while concurrently sputtering. It may be understood that these approximately circular race track patterns are indicative of the pattern of material that is ejected from the targets 110 a, b during the sputtering process. By keeping the race track patterns approximately circular (as opposed to elliptical), a more even deposition of material across the disks 104 a, b may be possible. In one embodiment, the approximately circular race track patterns may be formed such that, even if slightly elliptical, the major axis is not more than 20% larger than the minor axis. In another embodiment, the approximately circular race track patterns may be formed such that, even if slightly elliptical, the major axis is not more than 10% larger than the minor axis. In other embodiments, even tighter tolerances may be required. The approximately circular race track patterns may be achieved based at least in part on the regions 114 a, b of lower relative magnetic strength, which may compensate for the bucking effect between the magnetic rings 112 a, b, and allow the effective magnetic fields formed in part by each of the magnetic rings 112 a, b to be substantially symmetrical about their respective central axes.

The foregoing detailed description has set forth various embodiments of the systems and/or processes via the use of block diagrams, schematics, and examples. Insofar as such block diagrams, schematics, and examples contain one or more functions and/or operations, each function and/or operation within such block diagrams, flowcharts, or examples can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In one embodiment, the present subject matter may be implemented via Application Specific Integrated Circuits (ASICs). However, the embodiments disclosed herein, in whole or in part, can be equivalently implemented in standard integrated circuits, as one or more programs executed by one or more processors, as one or more programs executed by one or more controllers (e.g., microcontrollers), as firmware, or as virtually any combination thereof. 

I claim:
 1. A method of manufacturing magnetic disks, the method comprising: providing a sputtering system having a first target and a first magnetic ring associated with the first target, and a second target and a second magnetic ring associated with the second target, the first magnetic ring including a first region of lower relative magnetic strength positioned near the second magnetic ring, and the second magnetic ring including a second region of lower relative magnetic strength positioned near the first magnetic ring; positioning a first disk at a first sputtering location within the sputtering system, the first sputtering location associated with the first target; positioning a second disk at a second sputtering location within the sputtering system, the second sputtering location associated with the second target, the second sputtering location proximate the first sputtering location; generating a first electrical potential difference between a first anode and a first cathode associated with the first sputtering location; generating a second electrical potential difference between a second anode and a second cathode associated with the second sputtering location; and concurrently sputtering material from the first target onto the first disk and material from the second target onto the second disk.
 2. The method of claim 1, wherein the first cathode is electrically coupled to the first target, and the second cathode is electrically coupled to the second target.
 3. The method of claim 1, wherein the second disk is positioned such that a center axis of the second disk is approximately 15 cm apart from a center axis of the first disk.
 4. The method of claim 1, wherein generating the first electrical potential difference includes bringing the first anode to a ground potential and bringing the first cathode to a potential of less than −300 V.
 5. The method of claim 1, wherein the first target and the second target include magnetic alloys.
 6. The method of claim 1, wherein the first target and the second target include non-magnetic materials.
 7. The method of claim 1, wherein the first cathode is less than 3 cm apart from the second cathode.
 8. The method of claim 1, wherein the first magnetic ring includes a first plurality of permanent magnets, and the second magnetic ring includes a second plurality of permanent magnets.
 9. The method of claim 8, wherein the first region of lower relative magnetic strength includes at least one permanent magnet less than 10% weaker than other magnets of the first plurality of permanent magnets, and the second region of lower relative magnetic strength includes at least one permanent magnet less than 10% weaker than other magnets of the second plurality of permanent magnets.
 10. The method of claim 9, wherein the first region of lower relative magnetic strength includes at least one permanent magnet approximately 5% weaker than other magnets of the first plurality of permanent magnets, and the second region of lower relative magnetic strength includes at least one permanent magnet approximately 5% weaker than other magnets of the second plurality of permanent magnets.
 11. The method of claim 1, wherein the sputtering system further includes a first inner magnetic ring concentric with and positioned within the first magnetic ring, and a second inner magnetic ring concentric with and positioned within the second magnetic ring.
 12. The method of claim 11, wherein the first magnetic ring is oriented such that a north pole faces the first disk, and the first inner magnetic ring is oriented such that a south pole faces the first disk.
 13. The method of claim 1, further comprising eroding a first approximately circular race track pattern in the first target and a second approximately circular race track pattern in the second target while concurrently sputtering.
 14. The method of claim 1, further comprising concurrently sputtering material from a third target onto an opposite surface of the first disk and material from a fourth target onto an opposite surface of the second disk, while concurrently sputtering the material from the first target and the material from the second target. 